1. Field of the Invention
The present invention relates to an adapter power supply; and, more particularly, to an adapter power supply which can change an operation scheme of a switching unit into a PWM scheme or a quasi-resonant scheme depending on a normal operation mode and a standby mode.
2. Description of the Related Art
Since an adapter power supply of less than 60 W has a small capacity, a flyback converter or a forward converter has been used as a power stage. A voltage mode control technique or a current mode control technique has bee employed for controlling the converters.
Consumption power based on load conditions of the adapter power supply has been regulated in the market.
In particular, when there is no load, an adapter power supply has been regulated to have consumed power of less than 0.3 W.
To satisfy these conditions, a control Integrated Circuit (IC) must detect a no-load state, and controls consumption power to be minimized while maintaining an output voltage in the detected no-load state.
However, in the prior art, a switching unit operates at a fixed frequency according to a burst scheme, regardless of a mode. In the burst scheme, when an output voltage exceeds a predetermined range, it is judged that there is no load, and accordingly, the switching unit is turned off. Thereafter, when the output voltage is reduced to the predetermined range or lower, the switching unit is turned on again.
Therefore, when a standby mode is implemented in the prior art, the switching unit operates at the fixed frequency even in the standby mode according to the manner similar to that in the normal operation mode, so a large amount of switching loss is produced during the standby mode, and thus it is difficult to minimize standby power.